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The influence of erbium ion concentration on the optical properties of BaF2:ErF3 crystals was investigated. Four ErF3 concentration (0.05, 0.08, 0.15 and 0.5 mol% ErF3)-doped BaF2 crystals were obtained using the Bridgman technique. Room temperature optical absorption in the 250–850 nm spectral range was measured, and the photoluminescence (PL) and decay times were also investigated. The Judd–Ofelt (JO) approximation was used, taking into account four absorption peaks (at 377, 519, 653 and 802 nm). The JO intensity parameters, Ωt (t = 2, 4, 6), were calculated. The influence of the ErF3 concentration on the JO parameters, branching ratio, radiative transition probability and radiative lifetime were studied. The obtained results were compared with measured values and with those reported in the literature. Under excitation at 380 nm, the well-known green (539 nm) and red (668 nm) emissions were obtained. The calculated and experimental radiative lifetimes were in millisecond range for green and red emissions. The intensity of the PL spectra varied with the Er3+ ion concentration. The emission intensity increased linearly or exponentially, depending on the ErF3 concentration. Under excitation at 290 nm, separate to the green and red emissions, a new UV emission band (at 321 nm) was obtained. Other research has not reported the UV emission or the influence of ErF3 concentration on emission behavior. [ABSTRACT FROM AUTHOR]

Different doping concentrations of Dy3+/Tm3+ in ZrF 4 -BaF 2 -YF 3 -AlF 3 (ZBYA) fluoride glass samples were prepared by the melt-quenching method. Spectroscopic properties were analyzed through absorption (from 200 to 3300 nm) and emission spectra (from 1200 to 3200 nm). The spontaneous radiative transition probability, branching ratio and radiative lifetime of various energy levels transition were calculated based on the Judd-Ofelt theory. The emission cross-section value of the 1 mol% Dy3+/1 mol% Tm3+ co-doped ZBYA sample at 2.9 μm were calculated as 3.79 × 10−21 cm2. Near- and mid-IR emission spectra of Dy3+/Tm3+ co-doped ZBYA-fluoride glass under the excitation of 808 nm laser diode were investigated and discussed. Analysis of the emission spectra and the energy transition process of Dy3+/Tm3+ co-doped glass indicated that the introduction of Tm3+ ions can effectively improve the mid-infrared fluorescence intensity of Dy3+ ions, thus the Dy3+/Tm3+ co-doped ZBYA-fluoride glass can be an excellent candidate material for 2.9 μm mid-infrared laser applications. • Energy transfer processes between Dy3+ and Tm3+ ions in ZrF 4 -BaF 2 -YF 3 -AlF 3 (ZBYA) fluoride glass samples were investigated in details. • The transmittance of ZBYA glass at λ∼1000–6000 nm is as high as 90%, with an infrared cutoff wavelength at around λ∼9000 nm α OH − in the ZBYA sample is as low as ∼0.0098 cm−1, which is ascribed to the chemical dehydrating process (F− + OH−.→O2− + HF ↑) and longtime physical dehydrating process in ultra-dry pure nitrogen atmosphere. • The introduction of Tm3+ ions improve the mid-infrared emission intensity of Dy3+ ions in ZBYA glass, which is ascribed to the energy transfer process of Tm3+: 3F 4.→ Dy3+:6H 11/2. [ABSTRACT FROM AUTHOR]